Add threadpool deadlock fix to history for 5.4.0 [ci skip]

[cjlarose]

Description

I'm pretty sure History.md is mostly automatically generated and then manually cleaned up, but I think #2656 probably should've made the cut.

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• I have reviewed the guidelines for contributing to this repository.
• I have added (or updated) appropriate tests if this PR fixes a bug or adds a feature.
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[MSP-Greg]

JFYI, the automated 'history/changelog' code only adds PR's that have a label of one of the following. The mapping is in the same json file that contains the GitHub token, so it is repo specific, and can be changed.

bug
feature
perf
refactor

These are used to group them in the log. I thought that the code lists current PR's that are not labeled, I'll double check...

[MSP-Greg]

I'm fixing the code. Current code only lists PR's as 'bad' if there are no labels. The PR this adds (#2656) has a 'waiting for review' label, which is often removed immediately before the PR is merged.